See how combination of excelsheet calculation and industry-proven software can help you design your trayed column rigorously!

5/5 - (2 votes)

11/2023

viewers 455

5/5 - (2 votes)

11/2023

viewers 455

References

Requirement

1. Basic Math and Excel Skill

2. Koch-Glitsch Software

3. Have a Computer

4. Have a Desire

Description

Column Diameter Estimation

In this part the instructor shows how the following methods could be used to estimate column diameter

1. “C” factor method

This very simple method uses the Souders and Brown equation, which

gives the maximum acceptable vapor velocity below one tray to prevent

excessive entrainment of liquid from this tray to the tray above

Vm = maximum acceptable vapor velocity in the space below one tray,

(m/h),

ρl = liquid density at operating temp. and pressure of the tray (kg/m3),

ρv = vapor density at operating temp. and pressure of the tray (kg/m3),

C = Souders-Brown factor given by figure 12, in m/h versus tray spacing in

cm and liquid surface tension in N/m,

Usual tray spacing: 18 in (46 cm), 24 in (61 cm), 30 in (76 cm). 24 in

(61 cm) is the most frequent particularly for glycol and amine absorbers.

Actually, this spacing also depends on downcomer design.

Instead of figure 12, “C” factor values given by table as follows (from

Campbell – gas Conditioning and Processing) can also be used.

Manufacturers provide specific capacity factors for each proprietary use.

The column diameter of the column is given by equation as follows:

D = inside diameter of the column in meters,

Q = vapor flowrate at actual tray conditions (m3/h),

This method was originally developed for bubble cap trays and gives a

rough diameter value, especially for other types of tray.

2. Nomograph method for valve trays

Manufacturers of valve trays have developed design methods for their

trays. Design procedures are made available for preliminary studies.

Figure 13 is an example of such nomograph method which gives by

simple reading tray diameter with number of pass by tray. It requires the

knowledge for each tray of the liquid flow rate in m3/min and the vapour

load determined with equation as follows:

Detailed Method for Diameter Calculation

In this minute the trainer shows in a step-by-step procedure how the exact diameter using excel could be calculated.

Overview

Previous nomograph method corresponds to a first approach. It does

not take account of foaming which is the source of major problems in

many systems.

The Glitsch manual method for Ballast type valve tray gives results

with the following steps:

1st step: Determination of the flow path length (FPL)

An approximate flow path length is useful for establishing the minimum

column diameter.

With the values of the diameter (DT) and the number of pass (NP)

determined with the nomograph method (Figure 13), calculate the flow

path length (FPL) with equation as follows:

2nd step: Determination of Vapor Capacity Factor (CAF)

Figure 14 allows to determine the vapour capacity factor (CAFo) in

meter per second, versus vapor density and tray spacing for nonfoaming

fluids.

For foaming fluids this vapour capacity factor must be corrected by the

system factor value indicated in the table of figure 15.

3rd step:

Determination of the Downcomer Velocity (VDdsg)

The procedure used in this method for establishing downcomer area is

based on a “design“ velocity in meter per hour given by figure 16 for

non foaming fluid or by equation as follows:

4th step: Determination of Active Area (AAM)

The minimum active area is a function of vapor and liquid loads,

system properties, flood factor and flow path length.

The flood factor (FF) is used in certain equations for purpose of

estimating column size. It is the “design percent of flood” expressed as

a fraction.

A value of not more than 0.77 is normally used for vacuum columns

and a value not more than 0.82 is used for other services.

For demethanisers and near critical point values, it is recommended to

adopt a value in the range 0.6 to 0.7.

These values are intented to give not more than approximately 10 %

entrainment.

Higher flood factorsmay result in excessive entrainment and/or a

column sized too small for effective operation.

A flood factor of 0.65 to 0.75 should be used for column diameters

under 36″ (90 cm).

The minimum active area is determined with equation as follows:

Determination of Active Area (AAM)

5th step: Determination of the Downcomer area (ADM)

The minimum downcomer area is a function of liquid rate, downcomer

design velocity and flood factor.

If the downcomer area calculated by this equation is less than 11 % of

the active area (AAM) adopt for (ADM) the smaller value of relations as

follows:

6th step: Determination of the minimum inside diameter (DC) of the

column

The approximate column cross sectional area is calculated by

equations as follows:

The higher value is adopted.

Minimum inside diameter of the column (DC) in meters is calculated

with relation:

KG Tower Software

The instructor in this part aims to help process engineers to reach the followings :

-Become familiar with the environment of KG Tower software

–Know how to Calculate diameter of the tower using KG Tower

–Know how to Calculate other charachteristic of the disigned tower using KG Tower

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Equipment and Process Design

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